Method of electropolishing the internal surface of a hollow valve



9 K. M.BIV\RTL 'r 2,475,586

METHOD OF ELEGTR'OPOLISHI THE INTERNAL SURFACE OF HOLLOW VALVES -F'iledApril 9, 1945 Patented July 12, 1949 METHOD OF ELECTROPOLISHING THEINTERNAL VALVE SURFACE OF A HOLLOW Kenneth M. Bartlett, Cleveland, Ohio,assignor to Thompson Products Inc., Cleveland, Ohio, a

corporation of Ohio Application April 9, 1943, Serial No. 482,378

1 Claim. 1

This invention relates to a method of electropolishing the internalsurface of a hollow metal valve and to the hollow metal valve soproduced.

Hollow metal valves have heretofore been made by forging operations.After the valve has been forged, it is customary to ream out the stemportion of the valve to provide a relative smooth internal wall, andthen to polish the wall with abrasive paper. The result of these reamingand polishing operations has always been to leave an amorphous layerover the surface of the internal wall of the valve. Such an amorphouslayer, which is sometimes called a Beilby layer, is inherently formed asa result of any mechanical workin of a metal surface. One disadvantageof such a layer is that it has a relatively low grade of heat transfer,so that it to some extent obstructs the passage of heat from thecoolant, which may be metallic sodium, copper or the like, used in ahollow valve, to the wall of the valve and thence to the valve guide. Itis, of course, very desirable to provide the highest efliciency of heattransfer in order that the head of the valve may be kept as cool aspossible, to thereby prevent overheating of the valve.

I have now found that if the internal surface of a valve, or the like,is electropolished, a smooth, polished surface can be obtained that isentirely free from the objectionable amorphous layer produced by themechanical working of the metal of the valve. The result is that ahollow valve having an electropolished interior surface permits a moreeflicient transfer of heat from the coolant used in the valve to thestem portion of the valve, and thence to the external guides.

It is therefore an important object of this invention to provide amethod for electropolishing internal metal surfaces to insure a moreefficient rate of heat transfer through such surfaces.

It is a further important object of this invention to provide a methodfor the electropolishing of the internal surfaces of hollow metal valvesto eliminate or minimize the deleterious effect of scratches, remainingafter a final mechanical polishing or smoothing by the use of abrasivecloths, on the endurance strength of the valve by partially orwhollyremoving such scratches.

It is a further important object of this invention to provide a hollowvalve having an electropolished internal surface that is free from anyamorphous layer and that is characterized by a high rate of heattransfer. a a

Other and further important objects of this invention will be apparentfrom the disclosures in the specification and the accompanying drawings.

On the drawings:

Figure 1 is an elevational view, partly in section, of an apparatusembodying the principles of my invention and suitable for carrying out amethod of electropolishing the internal surface of a hollow valve; and

Figure 2 is an enlarged fragmentary, sectional view of the valve andattachment illustrated in Figure 1, with parts in elevation.

The reference numeral l0 indicates generally a support, having a base IIand an upright rod I2 extending from said base. A valve, indicatedgenerally by the reference numeral [3 is adapted to be supported fromthe stand It] by means of a clamping member l4, adjustably mounted alongsaid rod [2 by means of a thumbscrew I5. Said clamping member I4 isprovided at its free end with a ring [6 having an inner, annular liningll of rubber, or other insulating material. The valve I3 is adapted tobe inserted in said ring 16 at its stem end I8 to be frictionallysupported therein.

As illustrated, the valve l3 comprises a mushroom shaped head portion l9and an elongated stem portion 20. The head portion I9 is formed with acavity of a shape in general conforming with the external contour of thehead IS. The stem 20 is also formed with a cavity, indicated by thereference numeral 22, which extends for its full length and mergessmoothly into the head cavity 2|. Ordinarily, the valve 13 as it comesto the electropolishing step about to be described will have been reamedto produce the stem cavity 22. It may also have been mechanicallypolished, as by use of an abrasive cloth. It is advantageous that somemechanical means have been used that will leave the wall of the stemcavity 22 in a fairly smooth condition, relatively free from tool marks,since in that case the electropolishing step has less Work to do and canbe accomplished at a lower cost. Aside from this matter of cost, theelectropolishing method about to be described could be used even wherethe internal surface of the stem of the valve is relatively rough, sincein the electropolishing step the high points on the surface, or crests,are anodically dissolved away until, if the method is carried out for asufiicient length of time, the surface is left perfectly smooth and witha mirror polish.

Various metals and alloys may be employed in 39 and a rheostat 40.-

as Hastelloy steel; non-ferrous nickel-chromium alloys such asBrightray; and cobalt, chromiumand tungsten alloys such as Stellite. Itshould be understood, of course, that .theinvention herein described isnot limited to the use of these particular alloys. It should' 'furtherbe understood that the hollow valve'to which the method of my inventionis applied may be either forged, cast or otherwise formed.

As illustrated in Figure 1, a reservoir 23 for holding a supply of anelectrolyte 2d is mounted above the valve l3 from the ring stand in, bymeans of a clamping member 25-. Said reservoir 23, as illustrated,comprises a funnel having a stop cock 26 for controlling the rate offlow of the electrolyte.

The reservoir 23 is connected by means of a flexible hose 2i to atubular electrode 28 that extends into the hollow valve l3 for the: fulllength of the stem portion 20. The electrode 28 may'suitably besupported by a clamping member 29, adjustable upon the ring stand W. Aspacer 30 of insulating material is mounted in the stem end it) of thecavity 22 for spacing said electrode 28 equidistantly from the wall ofthe cavity 22. A second spacer 3i serves to center the lower end of saidelectrode 28. Both of the spacers 3t and 31 areprovided with openingstherethrough, such as the openings 32 and 33 respectively, which servefor the upward flow of the electrolyte that is introduced by the hollowelectrode 1 25 into the head cavity 2 i.

An electrical circuit, comprising lead wires 34 and 35, connected to asuitable source of electrical energy (not shown), is arranged to includethe valve I3 and the electrode 28. For this purpose, the lead wire34,connected to the positive side of a source of direct currentelectricity, is connected to the'valve l3 by means of a band connector36, and theneg-ative wire 35 is connected to the electrode 28 by meansof a screw tightened clamping band-31; A switch 38 is provided in thelead wire 34, as are also an armneter A voltmeter 4| is connected inparallel with the inner circuit through the electrolyte in the valve [3by means of a wire t2 extending across the lead-wires 34 and 35. As willbe evident fromthis description, the valve l3 itself forms the anode ofthe circuit that includes the electrolyte within said valve, While theelectrode 28 forms the cathode of the circuit.

Any suitable electropolishingelectrolyte may be used in the method-of myinvention. Among the electropolishingelectrolytes that are known tothose familiar with the art may be mentioned sulphuric and phosphoricacids, and [mixtures of the two. As a result of'considerable research,concentrated orthophosphoric acid at a-temperature between about 50 and150 F. has been found to give the most satisfactory results in theelectro-polishing of theinternal stem surface of a hollow valve made ofa chromium-containing steel, or one of alloys referred to above.Preferably, a 75% aqueous solution-of phosphoric acid, containing 75% oforthophosphoric acid by weight of the solution, and heated-to about 100F, is-emp1oyed= When-the cor-iditionsof operation hereinafter describedare followed, a mirrorlike, polished surface, free from any armorphouslayer, is produced by the use of 75% orthophosphoric acid. Otherelectrolytes, however, may be used satisfactorily, provided that theyare adapted to. electropolish the particular metal or alloy of which thevalve l3 ismade.

In operation, the electrolyte 24 from the reservoir 23 is allowed toflow through the stop cook 25 into the hollow'valve l3 at a suitablerate which is controlled by proper adjustment of the stop cock 26,. Theelectrolyte flows down through the hollow electrode 2.8 into the headcavity 2i of the valve and, afterfilling the valve, overflows throughthe opening 32 in the upper spacer 30, and runs down over the surface ofthe valve I3 into an overflow basin 43. After the valve I3 has filled upwith electrolyte, the rate of flow may be adjusted to about 2 cc. perminute.

As soon as the valve l3 has been filled with the electrolyte,-thecircuit comprising the lead wires 3% and 35 is energized by closingthe switch 38. A direct current capable of'delivering'an operatingvoltage of around 4 to 5 volts has been found suitable.- The rheostat isadjusted to give'a reading on the ammeter 39. of around-2.5 to 3.5-

amperes. Onthe basis ofthe internal surface of the 'valveundergoingelectropolishing, this will ordinarily give about 0.5:ampere per squareinch anode current density. If the anode current density is much greateror much less than-this, the rheostat 40. should" be adjusted to bringitwithin the limits mentioned.

The spacing ofthe anode'from the cathode is In 3 the apparatus illus--trated, the cathode electrode 28 may suitably be relatively important.

acopper tube having an outsidediameter of oneeighth ofan'inchandaninsidediameter of onesixteenth of an inch. With the usual diameters of thestem-caVity-IZZ', this williresult in an anodecathode spacing of.between one-eighth of an.

inch and three-eighthsrof an inch. These are, in general, the minimumandmaximum anodecathode spacings, for; optimum electropolishing results.The cathode electrode 28 need not be made of copper, but maybe. made ofstainless steel, Monel metal or other suitable metal or alloy.

The ratio of anode to cathode area should not vary. for best-resultsvery greatly from the ratio of 3.5. to 1.0. This ratioof anode tocathode area rather takes careof itself if :the anode-cathode spacing isproperly controlled as aboveindicated.

It is important, of course, that the cathode 28 thestem cavity 22 hasreceived a smooth, mirror like polish, or whatever degree of polish isdesired; With the conditions of electropolish-ing such as those abovedescribed, the entire electropolishing operation requires in theneighborhood of forty minutes: At-the -end'of this period,- the currentis shut off ahd thevalve l3 removed from-- its-clamping bracket I14,- emptied-=of the electrolyte' and thoroughly washeda The internalsur-'face-of the-stem cavity 22 will be" found to have takenone smooth,mirror-like polish and will be entirely free from any amorphous layer.

The electrolyte solution;-' may, ofcourse, be re-used; asbyreturning theexce'ssof electrolyte from the overflow receptacle backtothe res--ervoir 23. Upon continued use, the dissolved solids contents of theelectrolyte increases due to the anodic dissolution of metal from thesurface of the stem cavity 22, until finally the electrolyte is nolonger effective. This point is reached when about 0.17 gram of chromiumare present for each cc. of the electrolyte. The electrolyte may then beregenerated, or a new electrolyte used.

In my copending application, filed of even date herewith, I havedescribed a method and an apparatus for descaling the wall of the valvehead cavity, such as the cavity 2| of the valve l3. The descaling of thehead cavity, as described in this copending application for patent,would ordinarily be carried out before electropolishing the innersurface of the stem portion of the valve. If desired, apparatus such asshown in my copending application might be used for the electropolishingof the walls of the head cavity 21, using the operating conditionshereinabove set forth for the electropolishing of the stem portion ofthe valve. In the method as above described, however, very little, ifany, electropolishing of the walls of the head cavity takes place,because the cathode electrode 28 is relatively farther away from thewalls of the head cavity 2| than it is from the wall of the stem cavity22 and hence an insufficient amount of current passes through the wallsof the head cavity to effect polishing. The lower end of the cathodeelectrode 28 may, of course, be inserted into the stem cavity 22 foronly such distance as electropolishing of the stem portion may bedesired to be carried, or, by using the electrode extension of mycopending application, the walls of the head cavity 2| may beelectropolished, as well as descaled.

It will, of course, be understood that various ,details of constructionmay be varied through a wide range without departing from the principlesof this invention and it is, therefore, not the purpose to limit thepatent granted hereon otherwise than necessitated by the scope of theappended claim.

What I claim is:

The method of electropolishing the inner surface of the stem of a hollowvalve which comprises positioning a hollow electrode in said stem,flowing an electropolishing electrolyte through said hollow electrodeinto said valve while permitting the excess of said electrolyte tooverflow from said valve, making said inner stem surface the anode andsaid electrode the cathode, and while continuing said electrolyte flowpassing an electric current from said anode through said electrolyte tosaid electrode of sufiicient current density and for a suflicient periodof time to effect a polishing of said inner stem surface and to rendersaid inner stem surface free from any amorphous layer.

KENNETH M. BARTLETT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 883,756 Steiner Apr. 7, 19081,501,862 Midgeley July 15, 1924 1,850,426 Tyrrell Mar. 22, 19322,070,102 Weslake Feb. 9, 1937 2,332,569 Greenslade et al. Oct. 26, 19432,347,040 Faust Apr. 18, 1944 2,373,459 Colwell Apr. 10, 1945 FOREIGNPATENTS Number Country Date 335,003 Great Britain Sept. 18, 1930 577,030France May 26, 1924 OTHER REFERENCES Proceedings of The AmericanElectroplaters Society, 1941, pages 20 through 27, and 104 through 112.

The Metal Industry, Jan. 29, 1943, pages 69, 70.

